This invention relates generally to cigar lighter devices for automobiles and the like, and more particularly to lighters which are capable of heating to useful incandescence in relatively short intervals of time.
In the past, a large number of different cigar lighter constructions have been proposed and produced. In general, such lighters, if of the automatic variety, employed bimetallic spring fingers carried in a socket and which were engageable with the side surfaces of a heating element cup that was disposed at the inner end of the ignitor plug. When the plug was depressed, the fingers latched over the sides of the cup, establishing a circuit through the heating element. As the element reached useful incandescence, the bimetallic fingers became heated and would then spread and release the cup and the ignitor plug, enabling the same to retract and break the circuit through the element.
Numerous refinements to this basic structure have been achieved over the years. However, problems sometimes arose, as when one of the bimetallic fingers, for reasons sometimes obscure, shifted into the path of the ignitor plug while the latter was being depressed, resulting in breakage and possible short-circuiting of the socket. This led to either blown fuses or else burned-out wiring harnesses, depending on the degree of current overload protection built into the particular electrical system of the automobile. In other cases, the bimetallic fingers underwent an aging deformation after prolonged use. Under such circumstances, the socket usually had to be removed, in most cases involving work underneath or to the rear of the dashboard. Where the socket was not readily accessible, such repair or replacement was frequently difficult and time consuming.
Typically in automatic cigar lighters there is a time period of from ten to fifteen seconds following actuation of the ignitor plug, until the heating element reaches useful incandescence and the plug snaps out in readiness for use. In the past, efforts have been made to reduce this waiting time to just a few seconds. Generally, such innovative units have employed a bimetal disk disposed adjacent to the heating element, the disk constituting one contact of a switch which was adapted to quickly open after the element reached incandescence. By positioning the disk right next to the element, response times on the order of only several seconds have been achieved, particularly when an applied voltage which exceeded the continuous rating of the heating element was employed.
Prior lighters of both the automatic and manual variety, and of the type employing bimetallic disks all had a number of distinct disadvantages. Generally where the contact area of the disk was at its center, the socket was arranged to secure the disk at its periphery. The mounting for the disk had to to be such that it would not interfere with its flexing and snap-type movements. This imposed stringent requirements on the tolerances of both the disk and the part which carried it. Also, in most cases the disk constituted part of the "hot" side of the circuit, and thus had to be insulated from the remainder of the socket. Accordingly, such mountings were often awkward and prone to malfunction in use.
In other constructions, as where the contact area of the disk was at its periphery, the disk was mounted by means of a stud passing through a hole in its center, with the end of the stud being staked to hold the disk in place. The problem with this arrangement was that the support area was too small, and the disk eventually loosened, causing poor electrical contact with the stud. Or, if the support area was made sufficiently large, then the freedom of movement of the disk impaired, as was its proper functioning. In almost all such prior constructions, both the stud and the disk were current-carrying members, and any loosening caused either excessive voltage drops or else open circuits, resulting in malfunction or failure of the device. Where the bimetallic disk itself was employed as one contact of the circuit-breaking switch, there occured burning and pitting at the points of contact, this resulting in both a poor electrical connection and in deterioration of the disk itself, after a relatively short period of use. Moreover, where the disk was a current carrier, the relatively heavy current flow associated with such ignitor devices resulted in resistance-heating of the disk, aside from the heating effect due to its proximity to the heating element or coil. The resistance or self-heating effect depended on the resistance of the electrical path through the disk and stud; there were thus introduced other undesirable variables into the design of the lighter, which caused problems during manufacturing runs where large numbers of units were to be mass produced, from components possibly having slightly different physical and/or electrical characteristics.
Generally, the heating element of a cigar lighter is carried in a metal cup at the inner end of the ignitor plug. With spiral wound ribbon or coil type elements, the outermost convolution of the coil is as a rule secured by welding it to the annular wall of the cup. A rivet or stud with a slitted head is disposed in the bottom wall of the cup, with the other end of the coil being inserted and secured to such head. Since the cup constituted a current carrying member in the "hot" side of the circuit, special material was required in order to insulate it from the remainder of the ignitor plug, as well as from the rivet, which latter is in the "cold" side of the circuit. Various arrangements for mounting the cup and rivet were employed. Different combinations of insulating bushings and/or washers generally met with success, as a rule. But with such constructions, of course, care had to be exercised in the assembly, in order to insure proper seating of the washers, and to make certain that short-circuiting of the rivet to the cup would not occur.
U.S. Pat. No. 3,870,857 issued to Laurence G. Horwitt shows a recent arrangement for mounting a heating element cup and rivet, wherein the cup is insulated from the remainder of the ignitor plug by means of a mica washer. A series of nibs on the bottom wall of the cup is received in corresponding recesses in a transverse wall of the plug body, with the mica washer being sandwiched between the two walls. This permits the use of automatic assembly equipment, in that the nibs of the cup can become seated in the recesses of the transverse wall as a consequence of proper rotational orientation of the cup and plug body. This construction has met with wide acceptance and considerable success due to the savings of labor that were achieved while maintaining reliability.